The general objective of the proposed research is to understand the cellular mechanisms underlying the detection and signalling of light stimuli by vertebrate retinal photoreceptors. Specific goals are to study: 1) the nature of the transduction stages between light absorption by visual pigment and ultimate generation of an electrical signal, 2) factors that might influence the gain and time course of the transduction mechanism, 3) the electrical properties of the receptors, in particular the characteristics of the light-sensitive conductance with generates the electrical response, and 4) spontaneous excitation of visual pigments in darkness. The methods will involve mainly electrophysiological recording, using a new method which can record membrane current from a single receptor outer segment. This recording method has very high resolution and spatial discrimination and is especially suitable for studying visual transduction.